This command will just run an executable file on nix. Normally only executables which are installed from the package manager will work.

appimage-run is another option. Which can be used to run, you guessed it, appimages

Using a language server like nixd also helps a lot with auto completing packages and options in your config.

Apparently people are also working on the nickel configuration language to address some of the nix limitations and difficulties.

notify-send 'command finished!' works pretty well